People will be able to discern who is who based on avatars, merit count, merit history, signature, rank, and probably other things. The point is a random username won't do much if people can still find out who is who IMO. You would need to randomize everything.
This is kind of an interesting idea, but you're right about having to change (or obscure) all of the other details that'd make it possible to figure out who was posting. But even with a script like this, I'd imagine most members who wanted to make a post they thought would be controversial/reputation-damaging/whatever would do what they've always done and create a new account.
There are probably other applications for something like this, and props to OP for creating the script.
Ah, icopress....the days of being able to post as an anonymous guest are long gone. Not sure when Theymos did away with that, but I think it was before my time here.